/*
Authors:
  Bob Smith (bob@thestuff.net)
  Ben Maurer (bmaurer@users.sourceforge.net)
  Sebastien Pouliot  <sebastien@xamarin.com>

(C) 2001 Bob Smith.  http://www.thestuff.net
(C) 2003 Ben Maurer
Copyright (C) 2004 Novell, Inc (http://www.novell.com)
Copyright 2013 Xamarin Inc. (http://www.xamarin.com)

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/


namespace System
{
	public class Random
	{
		private uint x;
		private uint y;
		private uint z;
		private uint c;

		public Random()
			: this(123456789)
		{
		}

		public Random(int Seed)
		{
			x = (uint)Seed;
			y = 987654321;
			z = 43219876;
			c = 6543217;
		}

		private uint JKiss()
		{
			x = 314527869 * x + 1234567;
			y ^= y << 5;
			y ^= y >> 7;
			y ^= y << 22;
			ulong t = ((ulong)4294584393 * z + c);
			c = (uint)(t >> 32);
			z = (uint)t;
			return (x + y + z);
		}

		public virtual int Next(int minValue, int maxValue)
		{
			if (minValue > maxValue)
				return 0;

			// special case: a difference of one (or less) will always return the minimum
			// e.g. -1,-1 or -1,0 will always return -1
			uint diff = (uint)(maxValue - minValue);
			if (diff <= 1)
				return minValue;

			return minValue + ((int)(JKiss() % diff));
		}

		public virtual int Next(int maxValue)
		{
			if (maxValue < 0)
				return 0;

			return maxValue > 0 ? (int)(JKiss() % maxValue) : 0;
		}

		public virtual int Next()
		{
			// returns a non-negative, [0 - Int32.MacValue], random number
			// but we want to avoid calls to Math.Abs (call cost and branching cost it requires)
			// and the fact it would throw for Int32.MinValue (so roughly 1 time out of 2^32)
			int random = (int)JKiss();
			while (random == int.MinValue)
				random = (int)JKiss();
			int mask = random >> 31;
			random ^= mask;
			return random + (mask & 1);
		}

		public virtual void NextBytes(byte[] buffer)
		{
			if (buffer == null)
				return;

			// each random `int` can fill 4 bytes
			int p = 0;
			uint random;
			for (int i = 0; i < (buffer.Length >> 2); i++)
			{
				random = JKiss();
				buffer[p++] = (byte)(random >> 24);
				buffer[p++] = (byte)(random >> 16);
				buffer[p++] = (byte)(random >> 8);
				buffer[p++] = (byte)random;
			}
			if (p == buffer.Length)
				return;

			// complete the array
			random = JKiss();
			while (p < buffer.Length)
			{
				buffer[p++] = (byte)random;
				random >>= 8;
			}
		}

		public virtual double NextDouble()
		{
			// return a double value between [0,1]
			return Sample();
		}

		protected virtual double Sample()
		{
			// a single 32 bits random value is not enough to create a random double value
			uint a = JKiss() >> 6;  // Upper 26 bits
			uint b = JKiss() >> 5;  // Upper 27 bits
			return (a * 134217728.0 + b) / 9007199254740992.0;
		}
	}
}
